Ref 2- Introduction To Electrical Machines
EEE3441 Electrical MachinesDepartment of Electrical Engineering Lecture Introduction to Electrical Machines Vocational Training Council, Hong Kong.Week1
EEE3441 Electrical MachinesIn this Lecture Induction motors and synchronous machines areintroduced Production of rotating magnetic field Three-phase Induction motors Construction & operating principles Slip Characteristics & starting methods Three-phase synchronous machines Construction & operating principles Characteristics Vocational Training Council, Hong Kong.Week2
EEE3441 Electrical MachinesProduction of Rotating Magnetic Field Rotating Magnetic Field is very important to the operation ofelectrical machines, especially for 3-phase induction motor, andit is produced by three-phase voltages Three phase voltages has a phase displacement of 120 , henceat any instant of time there is a different voltage values in thethree phases The three phase voltage is sinusoidal in waveform Let us examine one complete cycle of a very low frequencythree phase voltage (period T 360 seconds), at an interval of30 electrical degrees, and we tabulate the three phase voltagesin the following table: Vocational Training Council, Hong Kong.Week3
EEE3441 Electrical MachinesInstantaneous Values of 3-φφ 10240270300330360 Vocational Training Council, Hong Kong.3 Phase Voltage 0086.6Week4
EEE3441 Electrical Machines Vocational Training Council, Hong Kong.Week5
EEE3441 Electrical MachinesMagnetic Field produced by three phase currents when 3phase voltage is applied to the stator of a 2-pole inductionmotorFinishPhase WindingStartStartAssume currentflows into thesewinding ends wheninput voltage ispositiveFinishStator of induction motorFinishStart Vocational Training Council, Hong Kong.Week6
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (1/13)Time : t 0Red phase 0 VYellow Phase -86.6 VBlue Phase 86.6 V Vocational Training Council, Hong Kong.Week7
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (2/13)Time : t 30 SecRed phase 50 VYellow Phase - 100 VBlue Phase 50 V Vocational Training Council, Hong Kong.Week8
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (3/13)Time : t 60 secRed phase 86.6 VYellow Phase -86.6 VBlue Phase 0 V Vocational Training Council, Hong Kong.Week9
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (4/13)Time : t 90 secRed phase 100 VYellow Phase - 50 VBlue Phase - 50 V Vocational Training Council, Hong Kong.Week10
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (5/13)Time : t 120 secRed phase 86.6 VYellow Phase 0 VBlue Phase -86.6 V Vocational Training Council, Hong Kong.Week11
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (6/13)Time : t 150 secRed phase 50 VYellow Phase 50 VBlue Phase -100 V Vocational Training Council, Hong Kong.Week12
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (7/13)Time : t 180 secRed phase 0 VYellow Phase 86.6 VBlue Phase -86.6 V Vocational Training Council, Hong Kong.Week13
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (8/13)Time : t 210 secRed phase -50 VYellow Phase 100 VBlue Phase -50 V Vocational Training Council, Hong Kong.Week14
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (9/13)Time : t 240 secRed phase -86.6 VYellow Phase 86.6 VBlue Phase 0 V Vocational Training Council, Hong Kong.Week15
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (10/13)Time : t 270 secRed phase -100 VYellow Phase 50 VBlue Phase 50 V Vocational Training Council, Hong Kong.Week16
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (11/13)Time : t 300 secRed phase -86.6 VYellow Phase 0 VBlue Phase 86.6 V Vocational Training Council, Hong Kong.Week17
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (12/13)Time : t 330 secRed phase -50 VYellow Phase -50 VBlue Phase 100 V Vocational Training Council, Hong Kong.Week18
EEE3441 Electrical MachinesMagnetic Field produced in a 2-pole induction motor (13/13)Time : t 360 secRed phase 0 VYellow Phase -86.6 VBlue Phase 86.6 V Vocational Training Council, Hong Kong.Week19
EEE3441 Electrical Machines3-phase Induction MotorConstructions and Operating Principles Vocational Training Council, Hong Kong.Week20
EEE3441 Electrical MachinesTwo types of 3-φ Induction Motor1. Squirrel Cage Induction Motor2. Slip-ring (wound) Rotor Induction MotorStator ConstructionStator construction is thesame for the two types ofinduction motorsStator windings Vocational Training Council, Hong Kong.Week21
EEE3441 Electrical MachinesSquirrel Cage Induction Motor (cross sectional view)Iron CoreFinishPhase WindingStartStartStator of induction motorFinishFinishSquirrel CageStartSquirrel cage Rotor Vocational Training Council, Hong Kong.Week22
EEE3441 Electrical MachinesSquirrel Cage Induction Motor– its rotor is in form of Squirrel CageECORNOFORIRHTAEPOVID FIELDRPICTONETGAMINGIRCUITCTRSHOGUM RININIMALUASTRDIE C NIUM BAMIALU Vocational Training Council, Hong Kong.Week23
EEE3441 Electrical MachinesSquirrel Cage RotorDie Cast Copper Rotor used in Energy-efficient Motors Vocational Training Council, Hong Kong.Week24
EEE3441 Electrical Machines3-phase Slip-ring (Wound rotor) Induction MotorRunning PositionBrushThreePhaseSupplyRotor WindingsStator WindingsExternal ResistorsSlip RingsStarting Position(Also called Wound Rotor Induction Motor) Vocational Training Council, Hong Kong.Week25
EEE3441 Electrical Machines3-phase Slip-ring (Wound rotor) Induction MotorSlip-rings Vocational Training Council, Hong Kong.Week26
EEE3441 Electrical Machines3-phase Slip-ring (Wound rotor) Induction Motor A slip ring rotor is wound with star connected three phasewindings, the winding ends are brought out and connectedto the exterior through three slip rings.The cage rotor is easy to manufacture, hence it is cheapand robust. However, we cannot do anything with therotor circuit, in other words we cannot control the speedor starting torque of a cage rotor.A slip ring rotor is expensive to manufacture and it isvunerable to overheat, but we can connect suitableexternal resistance through the slip rings to the rotorcircuit. As a result, we can control the starting torqueand running characteristic of the slip ring motor. Vocational Training Council, Hong Kong.Week27
EEE3441 Electrical MachinesOperating Principles of 3-phase induction motor A rotating magnetic field is produced when a threephase voltage is fed to the stator of a three phaseinduction motorThis rotating field will traverse the aluminium conductorsof the squirrel cage rotorAccording to Fleming‘s Right hand rule for generator,e.m.f. is induced in the aluminium bars of the squirrelcageAccording to Fleming‘s Left hand rule for motor, atorque is produced which will drive the rotor rotating inthe same direction as the magnetic field Vocational Training Council, Hong Kong.Week28
EEE3441 Electrical Machines Rotor Conductor ”cutting” by the Rotating Magnetic FieldRotatingdirection ofmagnetic fieldconductor of thealuminium cageFinishStartStartFinishFinishStartAt standstill Vocational Training Council, Hong Kong.Week29
EEE3441 Electrical Machines Induced current is produced and flowing in the closedrotor conductor circuit The direction of the induced current is determined byFleming Right Hand rule (Generation)Rotatingdirection ofmagneticfieldFinishStartStartFinishFinishN Vocational Training Council, Hong Kong.SStartRelativedirection ofmotion of thealuminiumcageconductorWeek30
EEE3441 Electrical Machines An electromagnetic force is produced by the interactionbetween the induced current and the rotating magnetic field Thus an electromagnetic torque turns the rotor to rotate. The direction of the electromagnetic torque is determined byFleming Left Hand rule (Motor)Rotatingdirection ofmagnetic fieldFinishStartStartFinishSDirection ofelectromagnetictorqueFinishNStart Vocational Training Council, Hong Kong.Week31
EEE3441 Electrical MachinesSpeed of Rotating Field Synchronous Speed [NS (rpm) or nS (rps)]We noticed that a complete sinusoidal cycle will causethe magnetic field produced to rotate a complete 360 in a two pole 3-phase induction motor.Since there are 60 seconds in one minute, the speed ofthe rotating field is equal to : 60 x frequencyA basic 2-pole induction motor has a set of threewinding groups installed in the stator (Red start &finish, Yellow start & finish and Blue start & finish) Vocational Training Council, Hong Kong.Week32
EEE3441 Electrical MachinesSpeed of Rotating Field For an induction motor with 4 poles, there are twosets of three winding groups installed in the stator,as a result, the magnetic field only rotates 180 forevery complete cycle of the sinusoidal waveform.Therefore, for an induction motor with p pole-pairs,the speed of the rotating field is given by:f( rps )pOR60 f( r pm )pf supply frequency and p No. of pole-pairs Vocational Training Council, Hong Kong.Week33
EEE3441 Electrical MachinesSlip The magnetic field of an induction motor rotates at asynchronous speed (Ns) which is equal to 60 fp This magnetic field will induce current in the rotor circuit,causing the rotor to run in the same direction as the fieldHowever, the speed of the rotor (Nr) is always slowerthan the speed of the field. Since if the speed of the rotoris equal to that of the field there will be no induced e.m.f.and there will be no driving torque to keep the rotorrunningSlip (s) is defined as Vocational Training Council, Hong Kong.Ns NrNsWeek34
EEE3441 Electrical MachinesExample of Slip CalculationCalculate the slip of an 8-pole, 3-phase induction motorrunning at 846 rpm. The frequency of the three phase supplyis 60 Hz.60 frequencySynchronous speed Ns pole pairs 60 604 900 rpmRotor speed Nr 846 rpmNs NrTherefore Slip Ns900 846 54 900900 0.06 Vocational Training Council, Hong Kong.Week35
EEE3441 Electrical MachinesSlip Equation Revisits Ns NrNss Ns Ns NrRotor SpeedSlip Speed(Speed of the rotatingmagnetic field cuttingacross the rotorconductors)(Speed of the rotor)Synchronous Speed(Speed of the rotating magnetic field)sf frequency Vocational Training Council, Hong Kong.Week36
EEE3441 Electrical MachinesTorqueTypical Torque / Slip Curve of Induction gionStartingTorqueS 1( Standstill ) Vocational Training Council, Hong Kong.SlipspeedS 0( Synchronous )speedWeek37
EEE3441 Electrical MachinesStarting Method of Induction MotorsA squirrel cage motor is at stationary before it is started, there is noback e.m.f. to oppose the current. Therefore, if this motor isconnected directly to the supply, will take an initial starting currentwhich is about 5 to 6 times of the full load value.Though this current decreases rapidly as the motor accelerates, itwill cause harm to the motor and will affect the voltage regulationof the power supply1. Direct on Line (DOL)Small motors up to the size of5 hp are allowed to be startedwith direct on line (DOL)starter Vocational Training Council, Hong Kong.MotorThreephasesupplycontactorWeek38
EEE3441 Electrical Machines2. Star-Delta Starter When the rating of the motor exceed 5 hp Some starting meansmust be used to start the motor. A star/delta starter is normallyused because it is the simpliest and cheapest type of starter. During starting, the stator winding is temporarily connected instar, therefore only phase voltage is applied to the stator. Thestarting current is reduced to 1/3 of the Direct on line startingcurrent. The starting torque, which is proportional to the startingcurrent, reduces also to 1/3 of the value at direct on line starting. After a period of about 5 seconds, the motor have accelerated tonearly full load speed. The stator winding is now reconnected asdelta, and full line voltage is applied each phase of the stator. Vocational Training Council, Hong Kong.Week39
EEE3441 Electrical MachinesSchematic Diagram of a Star-Delta StarterStatorRotorSupplyDeltaStarSwitchRunning Vocational Training Council, Hong Kong.StartingWeek40
EEE3441 Electrical Machines3. Auto-transformer Starter Some loads are very heavy and it will take a few minutesbefore it can run to full speed, these motors have to be startedby means of transformer starter.The reduced voltage during starting is obtained from thedifferent tappings (40% , 60% , 75%) of an auto-transformer.In the running condition, full voltage is applied to the statorand the transformer is cut out of the circuit.Auto-transformer StarterStartingRotorSupplyStatorWindingRunning Vocational Training Council, Hong Kong.Week41
EEE3441 Electrical Machines4. Starting of Wound Rotor Induction Motor The wound rotor (slip ring) induction motor can be started byinserting additional resistance in series with the rotor windingthrough the slip rings.In this way, maximun torque is obtained during starting. Theadditional resistance is cut off from the circuit as soon as the motoris started to avoid excessive power loss in the resistance.Running PositionBrushThreePhaseSupplyStator Windings Vocational Training Council, Hong Kong.Rotor WindingsSlip RingsExternal ResistorsStarting PositionWeek42
EEE3441 Electrical MachinesSynchronous machinesBasic construction A 3-phase synchronous machine is essentially composed ofa stationary stator and a rotating rotorThe stator is made of soft iron to provide the magneticfield a path with low permeability, the iron is laminatedto reduce eddy current and hysteresis iron loss. The statorhad a similar construction as that of a 3-phase inductionmotor. Three phase windings installed in the stator slotswhich are placed at 120 electrical degree apartThe rotor is an electromagnet placed inside the stator, therotor has the same number of poles as that of the stator.There are two types of rotor construction; the salient poleand the cylindrical rotor. Vocational Training Council, Hong Kong.Week43
EEE3441 Electrical MachinesThree phase synchronous generator The salient pole generator has a salient pole rotor structure,this machine is ideal for slow running power generation at50 - 60 Hz. The salient pole is wound with D.C. winding andcurrent is fed to the rotor via slip rings. The salient pole hasa nearly sinusoidal air gap so that the machine will producesinusoidal output.The cylindrical rotor generator has a cylindrical rotor, therotor is wound with windings fed with D.C. currents. Thenumber of windings in each slot is so selected that themagnetic flux is close to sinusoidal distribution. However,the output waveform is still polygonal in shape and there isa high harmonic contents in the generated voltage. Vocational Training Council, Hong Kong.Week44
EEE3441 Electrical MachinesSalient pole three phase synchronous generatorFinishPhase WindingNStartStartStator of synchronousGeneratorFinishFinishSStart Vocational Training Council, Hong Kong.Week45
EEE3441 Electrical MachinesSalient pole synchronous generator Advantages: The air gap between the stator and the rotor can beadjusted so that the magnetic flux is sinusoidal indistribution. As a result the output waveform will also besinusoidal in natureDisadvantages: The salient pole has a weak structure so that thismachine is not suitable for high speed application such asthe turbo-generator on air-plane.The salient pole generator is expensive Vocational Training Council, Hong Kong.Week46
EEE3441 Electrical MachinesCylindrical rotor synchronous generatorStator WindingFinishStartStartRotor windingfed with D.C.currentStator of synchronousGeneratorFinishFinishStart Vocational Training Council, Hong Kong.RotorWeek47
EEE3441 Electrical MachinesCylindrical rotor synchronous generator Advantages: The cylindrical rotor is cheaper than the salient pole rotor The cylindrical rotor is robotic in design, because it issymmetrical in shape, dynamically balance can be easilyobtained. Hence it can be used for high speed application, say,coupled to turbo-engine such as the generator in an air-craft.Disadvantages: The air gap is uniform for the rotor, the generated voltage willhave a polygonal waveform depending on the number ofwindings on each of the rotor slots. Though the shape of thepolygon is adjusted to be nearly sinusoidal, the outputwaveform still defers from the sine wave and therefore theharmonic content of the cylindrical rotor generator is highcompared with that of the salient pole design Vocational Training Council, Hong Kong.Week48
EEE3441 Electrical MachinesReasons for need of synchronous generator Dual voltages can be obtained from three phase supply; forexample, 380 V three phase line voltage for heavy powerapplications and 220 V single phase voltage for domestic and lightcurrent applications.It is more economic to use three phase power. Only threeconductors are required to transmit three-phase currents forbalanced three-phase load compared with six conductors for threesingle phase loads.A rotating magnetic field will be produced when three phasecurrents are fed to the stator of a 3-phase induction motor, thusproviding cheap and convenient mechanical power for industryThe synchronous generator can generate leading power factor kVAwhich can compensate the lagging power factor of the powertransmission system Vocational Training Council, Hong Kong.Week49
EEE3441 Electrical MachinesFIELDMO T(of co IONnductor)Fleming’s Right Hand Rule for generatorENTRRCU Vocational Training Council, Hong Kong.Week50
EEE3441 Electrical MachinesThree phase voltages produced by the salient pole generatorNSTime : t 0Red phase 0 VYellow Phase -86.6 VBlue Phase 86.6 V Vocational Training Council, Hong Kong.Week51
EEE3441 Electrical MachinesThree phase voltages produced by the salient pole generatorNSTime : t 30 SecRed phase 50 VYellow Phase - 100 VBlue Phase 50 V Vocational Training Council, Hong Kong.Week52
EEE3441 Electrical MachinesThree phase voltages produced by the salient pole generatorNS Vocational Training Council, Hong Kong.Time : t 60 secRed phase 86.6 VYellow Phase -86.6 VBlue Phase 0 VWeek53
EEE3441 Electrical MachinesThree phase voltages produced by the salient pole generatorNTime : t 90 secS Vocational Training Council, Hong Kong.Red phase 100 VYellow Phase - 50 VBlue Phase - 50 VWeek54
EEE3441 Electrical MachinesThree phase voltages produced by the salient pole generatorNTime : t 120 secS Vocational Training Council, Hong Kong.Red phase 86.6 VYellow Phase 0 VBlue Phase -86.6 VWeek55
EEE3441 Electrical MachinesSNThree phase voltages produced by the salient pole generatorTime : t 150 secRed phase 50 VYellow Phase 50 VBlue Phase -100 V Vocational Training Council, Hong Kong.Week56
EEE3441 Electrical MachinesSNThree phase voltages produced by the salient pole generatorTime : t 180 secRed phase 0 VYellow Phase 86.6 VBlue Phase -86.6 V Vocational Training Council, Hong Kong.Week57
EEE3441 Electrical MachinesNSThree phase voltages produced by the salient pole generatorTime : t 210 secRed phase -50 VYellow Phase 100 VBlue Phase -50 V Vocational Training Council, Hong Kong.Week58
EEE3441 Electrical MachinesThree phase voltages produced b
EEE3441 Electrical Machines Rotating Magnetic Field is very important to the operation of electrical machines, especially for 3-phase induction motor, and it is produced by three-phase voltages Three phase voltages has a phase displacement of 120 , hence at any instant of tim
character name character level deity homeland race size gender age height weight hair eyes campaign alignment player. head ref. other/notes character gear INVENTORY face ref. throat ref. shoulders ref. body ref. torso ref. arms ref. hands ref. waist ref.
Ref.ASTM D-3173-11 0.29 Volatile matter (%) Ref.ASTM D-3174-12 1.10 Ash (%) Ref.ASTM D-3175-11 98.40 Fixed carbon (%) Ref.ASTM D-3172-13 0.21 Bulk density (gm/cc) REF.IS:33-2002 0.631 NS analysis:N (%) Ref.ASTM D-4239-14 0.01 S (%) Ref.ASTM D-5373-14 0.01 SiO 2 (%) IS .
NGK X/Ref. 0383 BRIEF APPLICATION: Ford Fiesta, KA, Focus, Galaxy Part Number: PLB1375 O/E X/Ref. OZA659EE2 Fuel Parts X/Ref. LB1375 Bosch X/Ref. 258006127 NGK X/Ref. 0376 BRIEF APPLICATION: Landrover Freelander Rover 25 45 MGF Part Number: PLB1383 O/E X/Ref. OZA447E26 Fuel Parts X/Ref. LB1383 Bosch X/
Conjunto de tornillos de cabeza Allen Tornillo de cabeza allen DIN 912-8.8, acero cincado Ref. Nº 0957 084 . Contenido M 4 x 10 Ref. Nº 0084 4 10 100 unidades M 5 x 25 Ref. Nº 0084 5 25 5 0 unidades M 6 x 30 Ref. Nº 0084 6 30 25 unidades M 4 x 16 Ref. Nº 0084 4 16 100 unidades M 5 x 30 Ref. Nº 0084 5 30 50 unidades M 6 x 40 Ref. Nº .
Guide to the gods REF BL 473 .L43 1992 Handbook of Egyptian mythology REF BL 2441.3 .P56 2002 Handbook of Norse mythology REF BL 860 .L56 2001 Macmillan illustrated encyclopedia of myths and legends REF BL 303 .C67 1989 Mythologies REF BL 311 .D513 1991 National Geographic essential visual history of world mythology REF BL 312 .N38 2008
Ref. DWB 212 Extra Large Ref. DWB 213 Pegged Glenoids Small Ref. DWB 215 Medium Ref. DWB 216 Large Ref. DWB 217 Extra Large Ref. DWB 218 This surgical technique has been developed in conjunction with TOM NORRIS, M.D., (SAN FRANCISCO).
Electrical Infrastructure includes an electrical installation, electrical equipment, electrical line or associated equipment for an electrical line. 1.9 Electrical installation As per the Electrical Safety Act 2002 (s15) (a) An electrical installation is a group of items of electrical equipment that—
IB HL Biology Test: Topics 1 and 3 Answer Section MULTIPLE CHOICE 1. ANS: D REF: IB HL Bio Paper 1 TZ 1 May 2009 #2 2. ANS: A REF: IB HL Bio Paper 1 TZ 2 May 2010 #7 3. ANS: D REF: IB HL Bio Paper 1 TZ 2 May 2010 #13 4. ANS: A 5. ANS: B 6. ANS: C REF: IB HL Bio Paper 1 TZ 1 May 2009 #10 7. ANS: B REF: IB HL Bio Paper 1 TZ 1 May 2010 #1 8.
